Devices for measuring velocity and other kinematic parameters of a projectile using optical techniques are known. For example, U.S. Pat. No. 3,025,406 discloses a light screen which utilizes a pair of opposed mirrors which cause a light beam to make a zig-zag path across the screen. The apparatus disclosed in this patent is useful for detecting ballistic objects of small circumferential diameter that would otherwise pass through a monitoring area undetected.
U.S. Pat. No. 3,727,069 discloses an apparatus for measuring the velocity, size and location of a projectile, and includes vertical and horizontal arrays of light beams for indicating location and diameter of a projectile passing through a target frame. Two adjacent beam arrays are provided for measuring projectile velocity as a function of the time it takes for the projectile to pass through both arrays.
U.S. Pat. No. 4,128,761 discloses a ballistic velocity measuring instrument wherein a projectile passes through a first frame having photoresponsive devices and through a second frame also having photoresponsive devices to thereby provide a time-travel reference for a logarithmic diode circuit to compute projectile velocity.
Devices for measuring velocity and kinematic parameters of projectiles used in games such as baseball and golf are also known. For example, U.S. Pat. No. 4,177,994 discloses a golf practice device consisting of a grid of parallel, horizontal and vertical conductor wires which, when hit by a golf ball, cause a grid point contact between a vertical and horizontal wire. A light sensor determines when the golf ball is struck and starts a timing mechanism. The wire mesh detects both the position of the golf ball and stops the timing mechanism. Thus, when the golf ball strikes the grid, information is provided to permit calculation of the speed and position, and thus path of travel, of the travelling ball.
U.S. Pat. No. 4,199,141 discloses a baseball pitching scoring apparatus comprising a strike zone having surrounding ball zones. The zones include mechanical impact sensors or switches which provide a signal to a display means when hit by a ball. However, velocity of a ball cannot be determined by the disclosed apparatus.
U.S. Pat. No. 4,563,005 discloses a baseball pitching evaluation device comprising opposed infrared emitters and receivers which provide diagonal scanning rays or light pulses across a target zone to signal a computer which calculates the coordinates of a baseball crossing the target zone. As with U.S. Pat. No. 4,199,141, velocity of the baseball cannot be determined by the disclosed apparatus.
The known types of apparatus briefly discussed above have certain disadvantages. Systems using multiple parallel optical grids, while capable of measuring velocity, are expensive to construct, consume large amounts of electrical power, can be unreliable and may be unacceptably sensitive to variations and shadows in ambient lighting. Systems employing wire grids are mechanically complex, susceptible to damage from projectile impact and may not offer an acceptible compromise between accuracy, reliability and cost.
There is therefore a need for a device which can measure projectile velocity and impact which is inexpensive to construct, offers low power consumption, and has high reliability. The present invention fulfills that need.